The present invention relates to devices for the handling, storage and processing of chemical products intended for the chemical industries. In particular, it concerns mixers, processing devices and routing devices capable of handling highly corrosive products, such as concentrated acids or bases. In the present application, the expression xe2x80x9celements of chemical devicesxe2x80x9d means in particular, and in a collective manner, storage chambers, tanks, heat exchangers, reaction vessels, mixers, processing devices and routing devices.
More specifically, the invention relates to a manufacturing process for plated products, such as elements of chemical devices or assembly parts intended for the manufacture of elements of chemical devices, comprising at least one support part in metal and an anticorrosion metallic coating.
The chemical industries use numerous elements of chemical devices, which are needed for handling, storing and/or processing highly corrosive chemical products and which, consequently, have to be capable of resisting any corrosion from the latter.
In order to guarantee high resistance to corrosion, the elements of the chemical device usually comprise steel support parts and a metallic anticorrosion coating with a base of so-called xe2x80x9cnoblexe2x80x9d metals, such as titanium, tantalum, zirconium, a nickel-based alloy or stainless steel. The elements of the chemical device can be manufactured by assembling assembly parts, such as plates, previously coated with an anticorrosion metallic coating. The anticorrosion coating can be fixed to the support part in different ways, such as knurling, explosion cladding, hot rolling or simple covering without any join between the plate and the anticorrosion coating.
Certain applications, such as devices with low internal pressure, need a strong bond between the metal support part and the anticorrosion coating, that is to say a bond with high resistance to stripping, in order to avoid separation which could, for example, lead to collapsing of the anticorrosion coating. Knurling, explosion cladding and hot rolling make it possible to obtain very strong support/coating bonds, but these techniques cannot be used when the thickness of the anticorrosion coating is less than 0.7 mm.
Brazing makes it possible to obtain very strong support/coating bonds and reduce the thickness of the coating. However, brazing introduces additional difficulties. In particular, the difference in heat expansion coefficient between the substrate and the coating material (e.g. the expansion coefficient of steel is approximately twice as high as that of tantalum) results in the formation of mechanical stress. This stress weakens and deforms the coating. In addition, the brazing operation may induce the formation of intermetallic compounds liable to weaken the bond between the support and the coating. These difficulties are exacerbated by any shaping operations of the coated support part, particularly by means of plastic deformation.
The U.S. Pat. No. 4,291,104 held by Fansteel discloses the use of coatings comprising prior deformations referred to as xe2x80x9cconvolutionsxe2x80x9d in order to solve the random deformation problems induced by the differential expansions between the support and the coating. This solution does not prevent the formation of intermetallic compounds and reduces the area of the interface between the coating and the support, resulting in a weakening of the support/coating bond. In addition, this solution introduces serious problems for the subsequent shaping of the coated part. In particular, it is difficult to envisage rolling, between rollers, of large coated parts when the coating contains deformations. These deformations are also generally weakened by the crushing experienced during the shaping operations.
The applicant therefore looked for a method applicable to industrial development for fixing solidly a low thickness anticorrosion coating on a support part in metal, which enables subsequent deformation of the coated part and can be applied to large parts (typically plates wherein the surface is greater than approximately 1 m2).
The aim of the invention is a process for manufacturing a plated product comprising a support part in metal (preferentially steel) and an anticorrosion metallic coating, wherein the anticorrosion coating is fixed (fastened) on the support part by brazing under controlled atmosphere, in such a way as to obtain a mechanical link between at least one defined part of the support part and at least one defined part of the coating.
The applicant noted that the process according to the invention made it possible to fix solidly on a metallic part, particularly in steel, an anticorrosion coating with a thickness less than 1 mm, or even less than 0.5 mm, possibly less than or equal to 0.3 mm.
According to a first aspect of the invention, the plated product is an assembly part intended to manufacture an element of a chemical device. In this aspect of the invention, the manufacturing process comprises:
fixation by brazing, under a controlled atmosphere, of an anticorrosion coating on a support part (or xe2x80x9cunprocessed assembly partxe2x80x9d);
possible shaping of the coated part, by plastic deformation, in such a way as to produce a coated assembly part (or xe2x80x9cshape partxe2x80x9d).
According to a second aspect of the invention, the plated product is an element of a chemical device. In this aspect of the invention, the manufacturing process comprises:
fixation by brazing, under a controlled atmosphere, of an anticorrosion coating on at least one first and one second unprocessed assembly parts;
shaping of said coated parts by plastic deformation;
assembly of said parts (typically with operations including welding) in such a way as to form said element of the chemical device.
The invention is particularly advantageous when the assembly parts are shaped after having been coated with the anticorrosion coating, i.e. after fixation of an anticorrosion coating on the support parts (or xe2x80x9cunprocessed assembly partsxe2x80x9d). This alternative embodiment of the invention particularly makes it possible to simplify the handling, transport, storage and processing of coated parts. According to this advantageous embodiment of the invention, the surface of the unprocessed assembly parts intended to be coated is typically essentially plane. Said parts may comprise parts which have been previously shaped by machining, drilling, boring, plastic deformation or any other means.
In a preferred embodiment of the invention, the fixation of the anticorrosion coating is carried out by brazing at a temperature less than approximately 750xc2x0 C., and preferentially between 600xc2x0 C. and 720xc2x0 C., under a controlled atmosphere, which preferentially contains an inert gas in such a way as to prevent the oxidation of the coating during brazing. The applicant noted that using sufficiently low brazing temperatures made it possible to limit considerably the deformation of the coatings induced by the brazing operation and caused by differential expansion between the unprocessed part and the coating. It is then not necessary to pre-deform the coating to compensate for the differential expansion effect.